leclaireave

i have this GT Aggressor mountain bike and it takes 26 inch wheels. but, i have enough 27 inch and 700c wheels to equip a dozen GT Aggressors, and 1 26 inch wheel (the front wheel). the wheels fit onto the frame, but the brakes don't reach the rim. i'm wondering if anyone has made this work, and how. is there a part that works for this? did you think of some kind of mod? a conversion?

in the mean time, i fit a caliper brake system onto the rear which is better than nothing, but not much.

AEO

mavic v-brake adapter plate.

FBinNY 

+1 on the Mavic plate. I know a few people that used them to convert 26" to 700x (29") and all are very happy with the results.

leclaireave

oh ok, i see. this thing fits over the frame's original brake mounts and adds a second pair high enough to reach a 27 or 700c. the only lead i have so far and it seems alright... though i wish i could just use the frame's originals.

would it screw it the geometry or something to just make a longer brake arm?

FBinNY 

Ask kids who play on seesaws.

Canti and V-brake arms are simple levers. If you look at a V-brake arm the cable pulls from about 3 times farther from the fulcrum than where the shoe is. If you moved the shoe out another inch, doubling the distance to the fulcrum, you'd have to double the lengthen of the arm to maintain the same leverage.

leclaireave

oh alright, i see.

i guess it would look a little ridiculous, assuming it could be made to fit right... thanks

dabac

I wouldn't worry about looks.

In the eyes of the rest of the world all bike riders look like dorks, and a bike is a bike is a bike. Unless it's a trike or a recumbent, not many people would notice the difference.

No, the concern is functionality, WRT the leverage issue that FB mentions. When you change the leverage you also change the travel, and the stroke required by the brake lever to engage the brake properly. With longer brake arms you'd need more cable pull to get both proper engagement and rim clearance w/o the levers bottoming out against the bar or messing up the brake feel beyond what's manageable.
Doing custom levers would be possible, but quite a chore. One or perhaps two Travel Agents in series might give a decent enough ratio. Or a custom one.

leclaireave

every post leaves me saying, 'aaaaahhh yeaah.' as i was reading your reply it struck me what you were about to say. that's pretty clear now, i wonder what i was thinking before.

what's a travel agent? :\

fietsbob

Why not get an appropriate frame to use your road bike wheels ,
and leave the MTB with its 26" wheels as is?

FBinNY 

Not that it matters, but for the record.

If the brake shoe is moved farther from the fulcrum and the cable isn't he'd lose leverage and would pull less cable for for the same shoe movement. If the arms were lengthened to maintain the same approximate 3:1 cable:shoe distance the cable pull for fo r given shoe travel would be the same. At first glance you'd expect to need to pull more cable with the longer arms, but you don't because they travel in a shorter arc.

brockd15 

Not cheap, but the Paul Moto BMX brakes will let you swap to 700c and use the original canti studs. From the description on the website: "On a Pro sized BMX frame, the Moto BMX brake will work with both Pro and Mini (1⅜") sized rims. It even allows for 700c wheels on mountain bikes designed for 26" wheels."

https://www.paulcomp.com/motobmx.html

badamsjr

If functionality is your main concern, you might think about disc brakes. Avid BB7's come in MTB and Road flavors, so you can use whichever matches your levers. I put a Road BB7 on my touring bike with brifters, and it works great. My frame was not set up for disc, so I had to use the existing V-brake/booster/Travel Agent on the rear. It works fine for me. I had to get a disc fork, so took the opportunity to use a 29er disc fork (my frame is for 26") to raise the front a little, and 'slacken' the steering a touch.

BTW in the second pic, you can see the Travel Agent. It allows me to use road levers to operate a MTB brake. Gives a 2:1 or 1:2 ratio, depending on how you set it up. With the V-brake and Brake Booster, it is like having a 26" disc brake.

dabac

I actually ended up throwing some math on the issue - but you're right. If the brake arms would have had to swing through the same numbers of degrees he'd have been all out of luck, but for the same amount of pad travel it all works out.

Greyryder

I just checked the Paul's site, and their' Moto BMX V brakes are supposed to have enough reach to allow 700c wheels, on MTB frames made for 26" wheels. They're expensive, as V brakes go, but they'd allow you to use the original brake mounts.

The only other thing I'd know to suggest, would be Bombshell's VPS adapters, which do basically the same thing as the Mavic adapter.

ronp6

To use the existing mounts with any V brake that would work with a 700c would probably require changing the brake levers from linear pull to get the leverage back that you are losing. Either that or start sqeezing tenis balls now to get ready for spring. It is that seesaw thing; less travel, more pull.